This invention is directed to a post-crepe stabilized nonwoven material and a method of producing the same. More specifically, this invention is directed to a method of stabilizing a creped spunbond nonwoven web to provide increased tensile strength and enhanced appearance while minimizing the negative effects on bulk, permeability and other physical properties of the spunbond nonwoven web.
Creped thermoplastic nonwoven materials and methods for creping the nonwoven materials are known in the art. For example, a conventional process for creping a raw nonwoven fabric begins with coating the nonwoven fabric with a lubricant and then pressing the nonwoven fabric between a drive roll and a plate having a rough sandpaper-like surface. The raw nonwoven fabric is crinkled in a wavelike fashion in the direction of movement of the fabric by the frictional force caused by the pressing. The resulting creped fabric has wavelike crepes which contribute to softness. However, such conventional creping processes are not believed to be permanent.
The xe2x80x9cmicropleatxe2x80x9d structure of the creped fabric has a relatively low tensile modulus. As a result of this low tensile modulus, handling issues arise during the machine winding and the product conversion of the creped fabric. It is believed that the creping accomplished by conventional processes can be removed or reduced significantly by subjecting the creped fabric to mechanical stretching sufficient to flatten out the micropleat structure. Also, the creping is reduced during use of the fabric.
Thus, there is a need or desire for a creped thermoplastic nonwoven web having increased tensile strength sufficient to withstand the tensile or pulling forces experienced during the machine winding and product conversion processes.
There is also a need or desire for a method for producing a post-crepe stabilized nonwoven web with increased tensile strength and enhanced appearance without negatively effecting the bulk and permeability of the nonwoven web.
The present invention is directed to a stabilized creped nonwoven material or web having a limited extensibility in a machine direction and a method of producing the same. In accordance with this invention, the nonwoven web is creped and then thermally or heat stabilized. The stabilized creped nonwoven web has an increased tensile strength in a machine direction, which provides for easier machine winding and product conversion without damage to the nonwoven web due to tensile force or load associated with the machine winding and/or product conversion.
The stabilized creped nonwoven web of this invention is capable of withstanding a tensile force or load in a machine direction of at least about 2.0 lbs. at about 20% strain and a tensile force or load of at least about 5.0 lbs. at about 50% strain. Further, the thermal or heat stabilization process of this invention has minimal negative effect on the physical properties of the nonwoven web, for example bulk, permeability, and surface fiber loop structure. The thermally stabilized nonwoven web produced in accordance with this invention has an enhanced appearance due to the three-dimensional texture generated during a primary bonding step.
The method begins with providing any type of thermoplastic nonwoven web, including a spunbond web, a meltblown web, a bonded carded web, or a combination including any of the above. Desirably, the nonwoven web is a spunbond web.
The nonwoven web travels or moves through a primary bonder wherein the nonwoven web is thermally bonded, for example using a conventional calender roll. In accordance with one embodiment of this invention, the nonwoven web is thermally bonded using a Ramisch primary bond pattern. Any suitable conventional thermal bonding means may be used for thermally bonding the nonwoven web including, but not limited to, standard heat rolls, ultrasound and through-air-bonding.
After the nonwoven web is thermally bonded, the thermally bonded nonwoven web is creped. A first side of the nonwoven web may be creped using a first creping station wherein rollers nip the nonwoven web and guide it forward. As the rollers turn, a patterned or smooth printing roller dips into a bath containing an adhesive material, and applies the adhesive material to the first side of the nonwoven web. The adhesive-coated nonwoven web is then passed around a drying drum whereupon the adhesive-coated surface becomes adhered to the drying drum. The first side of the nonwoven web is then creped (i.e. lifted off the drum and bent) using the creping blade. Similarly, a second side of the nonwoven web may be creped using a second creping station, regardless of whether the first creping station has been bypassed.
The creped nonwoven web is passed through a post bonder wherein the creped nonwoven web is thermally or heat stabilized and wound onto a winding roll or storage roll. Post-crepe thermal or heat stabilization, including but not limited to through-air-bonding and embossing processes, produces the nonwoven web having improved stability and enhanced appearance while minimizing negative impacts on bulk, permeability, surface fiber loop structure and other physical properties of the nonwoven web.
The nonwoven web may be thermally stabilized using an embossing process. The creped nonwoven web is passed through a nip formed by an embossing or pattern roll and a smooth or second pattern roll. The pattern roll and/or the smooth roll may be heated using conventional means known to those having ordinary skill in the art. As the creped nonwoven web passes through the nip, the creped nonwoven web is. heated and embossed. Any suitable embossing pattern may be used to emboss the creped nonwoven web including a sine-wave embossing pattern, a machine direction (xe2x80x9cMDxe2x80x9d) line embossing pattern, and a cross-stars embossing pattern. Embossing patterns such as the sine-wave embossing pattern and the MD line embossing pattern provide a continuous embossing pattern or bond in the machine direction and, thus, provide for a stronger material in the machine direction than patterns which are not continuous in the machine direction.
Alternatively, the nonwoven web may be thermally stabilized using a through-air-bonding process. Desirably, the nonwoven web in accordance with this embodiment is made of bicomponent fibers. The polymer components of the bicomponent fibers have different melting points. As the nonwoven web is passed through a through-air-bonder, heated air is forced through the nonwoven web and the lower melting polymer component melts to bond the nonwoven web. Desirably, the air is heated to a temperature greater than the melting temperature of the lower melting polymer component but less than the melting temperature of the other polymer component. The through-air-bonding process produces the thermally stabilized creped bicomponent nonwoven web.
The resulting thermally stabilized creped nonwoven web has low density, high permeability, excellent surface and bulk softness, recoverable stretch properties, surface topology, and permanent out-of-plane fiber orientation. The stabilized creped nonwoven web can be used in a variety of end products including liners, transfer and surge layers, outercovers, wipers, and other fluid handling materials.
With the foregoing in mind, it is a feature and advantage of the invention to provide a post-crepe stabilized nonwoven web having increased tensile strength to withstand the forces experienced during machine winding and product conversion.
It is another feature and advantage of the invention to provide a post-crepe stabilized nonwoven web which has limited extensibility in a machine direction.
It is another feature and advantage of the invention to provide a method for producing the post-crepe stabilized nonwoven web having increased tensile strength without compromising the physical properties of the nonwoven web, including bulk, permeability and surface fiber loop structure.